mount rainier, Mount Rainier National Park, eruption column, lava, lava fountain, Law of Superposition, tephra, volcanic ash, Cascades Volcano Observatory
Students simulate tephra transport by placing ingredients in front of running fan, and mapping the resultant layers. This lesson plan is part of the "Living with a Volcano in Your Backyard" curriculum, created through a partnership between Mount Rainier National Park and the US Geological Survey Cascades Volcano Observatory.
Recognize how wind influences the dispersion pattern of tephra.
Understand the energy transformations that occur during tephra fall.
Recognize how volcano researchers assess the area of tephra fall.
What is tephra?
The term tephra refers to fragments of volcanic rock and lava of all sizes that are blasted into the atmosphere by explosions or carried upward in eruption columns or lava fountains. Large pieces of tephra fall to the ground first. Smaller pieces stay aloft for longer periods of time which allows the wind to blow tiny particles to a great distance from the volcano.
Volcanic ash refers to the tiniest pieces of tephra, smaller than 2 mm (0.1 inch) in diameter, which is a bit larger than the size of a pinhead. It is formed during explosive eruptions by the shattering of magma. Volcanic ash is not a product of combustion, such as ash formed by the burning of paper or wood. It is hard and very abrasive, mildly corrosive, and is electrically conductive, especially when wet.
Building tephra deposits
Once ejected into the air, the wind carries tephra particles. How far a tephra particle travels depends upon wind speed and size of the eruption. Coarse and heavy particles fall on or near the volcano; fine-grained, lightweight particles travel farther. The resulting tephra layer on the ground is progressively thinner and finer-grained with increasing distance downwind from the volcano. Viewed on a map, the plume trace and tephra layers are generally in the shape of an elongated oval. At high wind speeds the tephra layer is long and narrow. At lower wind speeds the tephra layer is shorter and wider. When there is no wind, the tephra deposit may be circular around the vent.
During successive eruptions tephra might fall in a similar pattern, overlapping or covering completely the older layer. Geologists establish the relative ages of layers by looking at the order in which the layers were deposited. As stated by the Law of Superposition, layers that are younger will be deposited on top of layers that are older.
Meteorological records show that at the Cascade Range volcanoes, the wind blows most often from west to east. This trend in wind direction during ancient eruptions is revealed in multiple tephra layers that are thickest on the east side of the Cascade Range.
The extensions in this activity provide opportunities for students to determine the path of volcanic ash after its eruption from a Cascade Range volcano.
Four clues to reading a tephra deposit
Geologists reply on four principal lines of evidence when they interpret tephra layers and identify their volcano of origin:
Tephra layers are thickest near and on the source volcano.
Coarse tephra falls to the ground before finer-grained tephra.
Younger layers overlie older layers.
A unique chemical signature exists at many volcanoes that allow researchers to match tephra with its source volcano. This fourth clue holds great importance to geologists, though it is not addressed in this activity.
Once your students understand these concepts and conduct the activity, they can be part of the volcano fan club!
Instructions and worksheets for students and teachers for use in the Volcano Fan Club lesson plan.
Copies of Student Page: "Volcano Fan Club - Instructions & Worksheet"
3 fans with 3-speed settings
3 checkerboard plastic table cloths or butcher paper or computer plotter paper similar in size to standard picnic table cloths
3 rolls of masking tape
3 sets of washable markers
1 cup cocoa powder
1 cup oatmeal
1 cup rice grains
1 cup cornmeal
brush or broom or vacuum cleaner
What to do before class begins:
Decide whether to conduct this activity with student groups or as a teacher demonstration, and whether you wish do multiple runs.
Select an area that is easy to clean and has enough space for all three experiment stations, 6 m x 1.5 m (20 ft x 5 ft).
For each experiment station, prepare 1 cup of each tephra sample (cocoa, cornmeal, oatmeal, and rice)- more if you plan to conduct multiple runs with varying conditions.
Blowing in the Wind
Simulate an eruption of tephra and analyze the resulting layers.
Tell students that once they complete this activity, they can become part of the volcano fan club!
Explain to students that they will make a series of tephra layers with household ingredients. They will collect, analyze, and graph data before presenting results to the class.
If conducting this activity with student participation, divide students into three groups and assign each group a station. Each group will simulate a different wind speed.
Distribute the student pages. Keep in mind that each square on the table cloth represents one square kilometer (or mile).
When students finish the experiments, and before cleanup, instruct each group to observe the other groups' "tephra" layers.
Instruct students to graph the distribution of the "tephra" layers, and to answer the questions on the student page.
Reassemble the class. Each group should present their results and graph to the remainder of the class. Discuss the similarities and differences in each group's results.
Lead discussion. In what ways does this experiment illustrate the four clues? How did wind speed affect the results? How does wind direction play a role in tephra distribution? How well does this activity illustrate the process of tephra dispersal from an eruption volcano? Why might tephra on the slopes of one volcano be found on the slopes of another? How might one eruption produce multiple tephra layers oriented in different directions? Hypothesize about what happens to tephra when it falls through rain.
Instruct students to show results of their experiment in stylized illustrations or to diagram their results on a whiteboard.
instruct students to use a computer spreadsheet program to construct their data table and graph.
Ask students to make their own tephra by crushing pieces of cereal to make different sizes of tephra.
Instead of a large fan, try using a hair dryer or hand-held mini-fan in the experiment.
Change the wind direction by setting the fan at an angle to the paper.
Add topography to the experiments. Instruct students to make hills and valleys by stuffing material under the table cloth or paper. Repeat the experiments and observe how topography affects tephra distribution.
Illustrate the concept by showing layers of various types of candy in a candy jar.
For assessment, instruct students to show results of their experiment in an illustration, or to diagram or graph the class results on a whiteboard. Review the student page results and look for evidence of student recognition that coarse materials fall first, followed by fine-grained material. Students should demonstrate ability to measure the area of the concentrated tephra; graph the data and interpret it. Instruct students to draw stylized diagrams of any tephra deposit formed by far-traveled winds, and by an eruption with no winds. Assess application to real-world situations by assigning interpretation of an additional ready-to-interpret data set of your choosing, and by asking questions about how this pattern of distribution might affect all regions of your state.
In the event of an eruption at Mount Rainier this activity displays the impact of tephra on surrounding areas.
Simulate effects of ash fall on a map landscape.
Simulate effects of ash fall on the region around a volcano. Obtain a large paper map that shows a volcano and surrounding landscape, including towns and cities, roads, airports, and other features. Place children's toy plastic animals, cars, trucks, airplanes, school buses, and emergency vehicles on the map surface. Set up a fan on the volcano to create wind. Simulate volcanic ash, either with the use of real volcanic ash, or fine silt or clay, cocoa powder, or flour. Students use a spoon to ladle the "ash" in front of the wind created by the fan. Students observe and discuss which areas are ash covered, and effects on animals, transportation, and communities. Research websites that describe the effects of volcanic ash.
Determine the path of volcanic ash using data at the American Meteorological Society's Data Streme website.
This extension requires students to possess some understanding about meteorological maps and atmospheric pressure and its control over wind direction and speed. Students estimate the travel direction and speed of an ash plume at a Cascade Range volcano. Instruct students to visit the American Meteorological Society's Data Streme web pages. At the website, students observe the wind speed and direction in the upper air above a Cascade Range volcano of their choice. They note the pressure levels for 850mb, 700mb, and 500mb, then assume that an eruption hurls volcanic ash to an altitude of six kilometers (~20,000 feet). Students make predictions about where the ash will travel to in 9 hours.
Frances, P., Oppenheimer, P., 2004, Volcanoes: Oxford University Press, 521 p.
Kenedi, C.A., Brantley, S.R., Hendley, II, J.W., Stauffer, P.H., 2000, volcanic ash fall— a hard rain of abrasive particles: U.S. Geological Survey Fact Sheet 027-00, 2p..
Myers, B., Brantley, S.R., Stauffer, P.H., and Hendley, J.W., 1997, What are volcano hazards? (revised March, 2008): U.S. Geological Survey Fact Sheet 002-97, 2p.